Due to requirements, for example, for obtaining superior dynamic characteristics or saving weight, FRP, in particular, carbon fiber reinforced plastics (hereinafter referred to as “CFRP”) have been used primarily for members used in the fields of the space and aircraft industry or sports industry. For example, the FRP described above have been used for members of the space and aircraft applications, which include primary structural materials (fuselages, main wings, tail units, wing ribs, and the like) and secondary structural materials (fairings, control surfaces, trailing edges, and the like) for small and medium airplanes, large passenger aircraft, military aircraft, space shuttles, and the like.
The previous technical subjects in the fields described above were primarily improvements of dynamic characteristics or higher accurate assembly of FRP; however, the recent subjects have been the production of larger FRP and the thorough production cost reduction thereof. As application fields of FRP mentioned above develop broadly to almost all transport facilities (railroad vehicles, automobiles, ships and vessels, and the like) and general industries (wind power, civil engineering, architecture, and the like), more cost reduction of FRP is required strongly.
As a typical method for manufacturing a FRP member having superior dynamic characteristics, an autoclave molding method has been known. In the autoclave molding method, prepregs composed of reinforcing fibers and a matrix resin impregnated therein beforehand are laminated to each other in a molding die and are then heated and pressed, thereby forming a FRP. When the prepregs are used in this method as an intermediate member, a FRP having significantly superior quality can be advantageously formed. However, in addition to high cost required for the formation and storage of the prepregs, since the molding equipment therefor becomes larger, the productivity of FRP according to this manufacturing method has not been so high.
As a manufacturing method of a FRP having superior productivity, for example, a vacuum resin transfer molding (vacuum RTM) method may be mentioned. According to the vacuum RTM method, reinforcing fibers not impregnated (dry) with a matrix resin are placed in a molding die having a complicated shape, and in the state in which the inside of the molding die is evacuated, the matrix resin is forcedly injected in the molding die with a pressure so that the fibers are impregnated with the matrix resin, thereby molding a FRP.
In this vacuum RTM method, in particular, when a large structural body is molded, since timing of injecting a resin from a plurality of resin injection ports, which are provided for the molding die, must be appropriately controlled, it is extremely important to understand the exact position of the flowing resin. In addition, when a large molded body which requires a plurality of injection ports as described above is formed, after a reinforcing fiber base material is placed in a bottom mold, the cavity thereof is covered with a transparent bagging film and is evacuated, and subsequently the resin is sequentially injected from the injection ports. In this case, while observing the flowing resin through the transparent bagging film, an operator optionally performs the injection of the resin at appropriate timing.
However, when the flow condition of the resin is observed by an operator as described above, some place may become difficult to be observed when a molded body is large, or the position of a front end of the flowing resin may be misunderstood in some case, and hence a problem may arise in that the injection of the resin cannot be performed at appropriate timing. Furthermore, when a molded body having high heat resistance is manufactured using the bottom mold and the bagging film described above, since the entire mold is heated to a high temperature, it becomes difficult for an operator to observe the flow of the resin by standing beside the mold, or when molding is performed by using a two-sided mold, the flow condition of the resin cannot be observed at all from outside the mold by an operator even when a molded body is relatively small. Accordingly, as a result, a problem may arise in that timing of injecting the resin from a plurality of injection ports cannot be determined. In the cases described above, while the flow velocity of the resin is being estimated, the timing of injecting the resin from a plurality of the injection ports has been determined by the intuition of an operator formed through experience and in consideration of the amount of the resin prepared beforehand. However, by the method described above, there have been problems in that the reliability is low, the probability of mass production is low, and the productivity is low.